Interconnected Pressure Estimation and Double Closed-Loop Cascade Control for an Integrated Electrohydraulic Brake System

In this article, a novel double closed-loop cascade control architecture with interconnected pressure estimation for a pressure-sensor-unequipped integrated electrohydraulic brake system suitable for automobile applications is presented. Starting from a control-oriented model, an interconnected pressure estimator is employed to estimate the pressure dealing with the nonlinear pressure-position relationship. To reduce the negative influence of system nonlinearities and uncertainties, i.e., friction, pressure-position relationship, brake pad wear, temperature variation, knockoff, a double closed-loop cascade controller is proposed. An outer pressure tracking loop employs sliding mode controller (SMC) with conditional integrator to ensure tracking accuracy with desired position of master cylinder piston as control output; an inner position control loop is designed using the SMC to improve the response speed. By this way, the bandwidth of inner position is wider than the outer pressure loop, which has advantages in quickly eliminating the disturbances caused by system nonlinearities and uncertainties. The overall system asymptotic stability is analytically investigated through the Lyapunov Theorem. Simulation and experimental validation demonstrate excellent tracking performance and robustness.